instruments, and then dividing the charge with the other, found that
when air intervened in both cases the charge was equally divided.
But when shellac, sulphur, or spermaceti was interposed between the
two spheres of one jar, while air occupied this interval in the
other, then he found that the instrument occupied by the 'solid
dielectric' takes more than half the original charge. A portion of
the charge was absorbed by the dielectric itself. The electricity
took time to penetrate the dielectric. Immediately after the
discharge of the apparatus, no trace of electricity was found upon
its knob. But after a time electricity was found there, the charge
having gradually returned from the dielectric in which it had been
lodged. Different insulators possess this power of permitting the
charge to enter them in different degrees. Faraday figured their
particles as polarized, and he concluded that the force of induction
is propagated from particle to particle of the dielectric from the
inner sphere to the outer one. This power of propagation possessed
by insulators he called their 'Specific Inductive Capacity.'

Faraday visualizes with the utmost clearness the state of his
contiguous particles; one after another they become charged, each
succeeding particle depending for its charge upon its predecessor.
And now he seeks to break down the wall of partition between
conductors and insulators. 'Can we not,' he says, 'by a gradual
chain of association carry up discharge from its occurrence in air
through spermaceti and water, to solutions, and then on to chlorides,
oxides, and metals, without any essential change in its character?'
Even copper, he urges, offers a resistance to the transmission of
electricity. The action of its particles differs from those of an
insulator only in degree. They are charged like the particles of
the insulator, but they discharge with greater ease and rapidity;